As previously mentioned, distribute lists can be used to filter routing updates on a per-interface basis, or by filtering routes for redistribution.
Filtering for redistribution example:
Filtering routing updates on an interface example:
Typical usage is distribute-list out for filtering redistribution from another process, or distribute-list in for filtering inbound routing updates on an interface. The former can also be used to filter outbound routing updates on an interface.
Caveats:
- distribute-list out cannot be used with link-state routing protocols to block outbound LSAs on an interface.
- Filtered routing updates from an OSPF neighbor are still placed into the OSPF database, but not added to the routing table.
Stuck-in-Active: Journal of an IT-Network Administrator 